1. Field of the Invention
The present invention relates to ultrasonic motor driving methods and ultrasonic motors.
2. Description of the Related Art
Recently, the use of ultrasonic motors of more compact size, higher torque, longer stroke, and higher resolution than electromagnetic motors has greatly increased.
Such ultrasonic motors are designed such that an ultrasonic vibrator is pressed, via a driving part serving as a frictional member, against a driven member serving as a member moved relative to the vibrator. This produces frictional force between the driving part and the driven member, thereby driving this member.
The technique of driving an ultrasonic motor efficiently and stably for a long time is disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 10-191658.
This publication discloses a vibrating actuator that includes: a vibrator; and a driven member disposed in pressurized contact with the vibrator and moved relative to the vibrator. The vibrating actuator has an adhered material removal area defined in a predetermined part of either one of the contact faces between the vibrator and driven member or predetermined parts of both of the contact faces, to remove material adhered to the contact faces.
The technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-191658 makes the surface roughness of the adhered material removal area greater than that of the other drive areas, thereby removing wear particles clinging to the contact faces at the adhered material removal area.
However, in the vibrating actuator in Jpn. Pat. Appln. KOKAI Publication No. 10-191658, the area including the adhered material removal area is a fixed drive range of a driving part (i.e., a driving force output portion of the vibrating actuator in the publication) in a regular drive period.
Accordingly, even after wear particles clinging to the driving part are removed at the adhered material removal area, the wear particles may be pulled into another drive range, that is, the regular reciprocal drive range.
The technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 10-191658 has not yet completely overcome the foregoing problem that wear particles are caught between the driving part and the driven member, with the result that the speed of the driven member drops and as the driving part moves over the wear particles it ends up stopping the driven member.